This invention relates to the improved manufacture of fibrillated material webs, and particularly to pinned rollers suitable for making fibrillated film from polyolefin base resins for filter material. More particularly, this invention reates to an improvement on the methods and apparatus of U.S. Pat. No. 3,880,173, the disclosure of which is hereby incorporated by reference.
It is known to fibrillate a poleyolefin film to produce a film having an interconnected fibrous network. The process involves stretching the film to orient the polymer chain or crystal structure to be aligned in the direction of the advancement of the film, and subjecting the oriented film to impaction by various means to fracture the film and create the fibrous network. Orientation is typically accomplished by stretching the web using rollers that are rotating at different surface speeds. The means to impact the oriented films may include fluids such as water or gas jets, blades, pins, toothed projections, laser beams, twisting of the orientated films, embossing of the orientated films, and embossing of the films prior to orientation.
Prior U.S. Pat. No. 3,880,173 and corresponding U.K. Patent 1,442,593 refer to obtaining fibrillated polyolefin film materials for filter materials as an alternative to cellulose acetate filter materials, specifically, but not exclusively, for filtering tobacco smoke of smoking articles. The polyolefin materials described include polypropylene, polyethylene, or a mixture thereof, or a copolymer of propylene and ethylene, and optionally may include finely divided whitener such as titanium dioxide to facilitate the production of narrow fibrous strands.
In accordance with the fibrillation process described in U.S. Pat. No. 3,880,173, the polyolefin stock materials are heated, mixed, and extruded into a thin film. The film is blown to form thinner films which are flattened, slit lengthwise, and superimposed to form multiple thin film layers of about 10-15 .mu. thick. The multiple layers are passed through an oven at elevated temperatures while being stretched over differential speed rollers to orient the molecular structure of the films in the longitudinal direction. The oriented film is then passed over a rotating roller having a plurality of pins projecting therefrom.
The pinned roller rotates at a surface speed that is faster than the linear speed of the web. The pins projecting from the roller thus contact and fracture the relatively slower moving superimposed layers, thereby producing an interconnected web of fibers having free ends that is the fibrillated material. The fibrillated material is then passed into a stuffer box crimper device in a conventional manner to create crimps in the fibrillated film, thus forming a polyolefin tow. The crimps include primary crimps, the creation of a wavy configuration in the fibers caused by rapid deceleration of the advancing fibers, and a secondary crimp, corresponding to a wrinkling effect when the fibers collapse and fold in on themselves.
For forming filters for smoking articles, the secondary crimp is typically removed from the polyolefin tow, for example, by tension, and the tow is formed into a bloomed flocculent mass which is then formed into a filter rod by using a conventional filter rod making machine. A binder agent, e.g., vinyl acetate, may be included in the tow for forming filter rods in a known manner.
One problem with the known fibrillated polyolefin materials is that, although they may have filtering characteristics comparable to cellulose acetate filters, they do not have the low mass that is required to provide a cost advantage. Another problem is that known tows do not have a consistent, quality fibrous network that allows for use in a filter tow material where relatively short lengths of tow are used. Another problem is that the known apparatus for producing the fibrillated network consumes a substantial amount of power and generates a substantial amount of noise to create the interconnected fiber network.
Further, notwithstanding years of development efforts, there is no commercial use of a filter for smoking articles comprising a fibrillated polyolefin material that provides the advantages and benefits associated with conventional cellulos acetate filter materials used in smoking articles, and particularly, tobacco-containing cigarettes.
Accordingly, there is a continuing need for apparatus and methods for fibrillating polyolefin resin based materials to produce a fibrillated tow material having a consistent fibrous strand network that is adaptable for use as a filter tow material, particularly for filtering tobacco smoke, that is more effective, and easier and cheaper to manufacture and form into filters, than cellulose acetate.